There is a blog that I would care never to read again, even in moderation. I added the blog to my localhost list so now I can't visit the blog anymore. But my lizard-brain has found a workaround: if I google the blog I can read Google's cache. Is there a way to block Google's cache of the blog without blocking the rest of Google's functions?

Depends on the amount of effort you are willing to spend. I have a local Squid caching proxy (maybe privoxy or 3proxy or something else is better for you), I have set up URL rewriting and among other things I block some URL patterns for various reasons. It is not too hard to set up and there are various ways to do this with various proxies.